The invention relates to a joining method on a jet spinning machine, as well as a spinning device and a jet spinning machine for carrying out the joining method.
Jet spinning machines generally comprise spinning devices, to which a fibre band drawn to a fibre bundle is supplied from a drawing frame. The fibre band runs through a spinning nozzle, in which it is acted upon by swirling air currents and is thereby provided with a true torsion or true twist. Positioned downstream from the spinning nozzle is a hollow spinning cone, through which the fibre band is drawn off as a thread from an outlet opening and then wound onto a take-up bobbin as the upper thread.
German Patent Publication DE 3611050 A1 describes a spinning unit, which is intended to produce bobbins being used a feed bobbins for twisting. Substantially untwisted thread components are wound onto the feed bobbins. For joining, two auxiliary threads are in each case drawn off from an auxiliary bobbin. The ends of the auxiliary threads are transferred with the aid of thread clamps to a suction device and then placed by the thread clamps in a draw-off mechanism configured as a pair of rollers, then into the false twist mechanism and finally, from the side, into the pair of withdrawal rollers of a drawing frame. The activated false twisting mechanism acts upon the auxiliary threads with a false twist. The auxiliary threads transport the false twist counter to the thread running direction to the withdrawal rollers of the drawing frame. For joining, a fibre strand is fed onto the running auxiliary threads, in each case, from the drawing frame. The auxiliary threads and the fibre strand supplied to them in each case are now together provided with a false twist by the false twist mechanism from the withdrawal rollers of the drawing frame to the false twist mechanism. The spinning unit of German Patent Publication DE 3611050 A1 is not suitable for producing a spun thread with a true twist. Inserting the auxiliary threads according to the disclosure of German Patent Publication DE 3611050 A1, from the side, is not possible when using jet spinning devices, which operate with a twist retaining mechanism and a hollow spinning cone.
A jet spinning machine is described in European Patent Publication EP 1 072 702 A2, as prior art, in which during a start or when a thread breaks the end of the upper thread is transported by means of a transfer arm into the vicinity of the outlet opening of the spinning cone designated a spindle. From there, the upper thread runs from the direction opposed to the thread delivery side through the spinning cone and the spinning nozzle and is sucked into a suction element. The fibre bundle on the delivery side, which exits from the drawing frame is also sucked into the suction element and intertwined with the upper thread. The two intertwined threads are then sucked into the spinning nozzle for connection. In this method, the upper thread has to be advanced from the spinning device to the suction element in the direction opposing the spinning operation. During this preparation phase for thread connection, errors frequently occur which disturb the formation of a thread connection or even prevent it. A further disadvantage is that the thread portion, which contains the connection between the upper thread and thread bundle is clearly recognisably thicker than the remaining thread. A thick location of this type has a disruptive effect in the end product, for example a woven fabric and is a quality defect. Apart from the disadvantage that the thread connection process is frequently unsuccessful, the length of the thread portion, which forms the piecer can hardly be controlled. Approximately the same lengths of the piecer are not ensured.
In order to overcome these problems, European Patent Publication EP 1 072 702 A2 proposes a spinning device for an alternative joining method. This spinning device has a spinning cone with joining nozzles close to the tip and an axially extending spinning thread channel, through which the spinning thread is drawn off. The spinning thread channel widens towards its thread outlet side in a stepped manner. These joining nozzles are used to generate swirling air currents in the spinning cone by means of supplied compressed air, by means of which a reduced pressure is generated at the tip of the spinning cone. If compressed air acts on the conventional spinning nozzles and also the joining nozzles arranged downstream from the spinning nozzles in the spinning cone, the fibre bundle supplied by the drawing frame is firstly acted upon by a rotational flow and conveyed to the mouth of the spinning thread channel at the tip of the spinning cone. Owing to the reduced pressure produced there by the activated joining nozzles, the fibre bundle is sucked into the spinning thread channel, acted upon by a rotational flow revolving counter to the spinning nozzles when passing through the joining nozzles and transported by the outflowing compressed air to the thread outlet end. The joining nozzles provide the fibre bundle with a false twist briefly during joining. Once the thread has reached the take-off rollers arranged downstream from the spinning cone and is clamped there, the joining nozzles are deactivated, and a normal thread with a true twist is then spun. The thread portion which has been spun with a false twist, is cut off and the end of the newly spun yarn is connected to the end of the upper thread drawn off from the take-up bobbin by a splicing device.
So the tip of the fibre bundle can be sucked into the spinning cone during the joining process, the bore diameter of the mouth of the spinning thread channel has to have a minimum size, which is, for example, a diameter of 1 mm. The limitation of the bore diameter leads decisively to limitations in the influencing of the yarn character.